Evening Primrose Oil Should NOT Be Used for Cervical Ripening
Evening primrose oil is not recommended for cervical ripening in term pregnant women, as current evidence shows it is ineffective and may be associated with adverse outcomes. 1
Evidence Against Evening Primrose Oil
Lack of Efficacy
A 2021 systematic review and meta-analysis of four randomized controlled trials found no significant difference in Bishop score improvement between evening primrose oil and control groups (SMD: 0.27,95% CI: -0.41 to 0.96, p = 0.43), demonstrating that oral evening primrose oil does not effectively ripen the cervix. 2
A 2018 triple-blind randomized controlled trial in 80 nulliparous women at 40 weeks gestation showed no significant differences between evening primrose oil (1000 mg twice daily for 7 days) and placebo in terms of Bishop score, gestational age at delivery, need for labor induction or augmentation, duration of labor stages, or neonatal outcomes. 3
A 1999 retrospective study of 108 low-risk nulliparous women found that oral evening primrose oil from 37 weeks until birth did not shorten gestation or decrease overall labor length. 4
Potential Harms
The same 1999 study revealed that evening primrose oil use may be associated with increased incidence of prolonged rupture of membranes, oxytocin augmentation, arrest of descent, and vacuum extraction. 4
The American Family Physician explicitly states that the use of evening primrose oil during pregnancy is not supported in the literature and should be avoided. 1
Contradictory Single Study
One 2024 randomized controlled trial (48 participants per group) reported higher Bishop scores after vaginal evening primrose oil 1000 mg daily compared to placebo (5.83 ± 1.68 vs 5.19 ± 1.52, p = 0.002), with reduced need for oxytocin and amniotomy. 5 However, this single small study contradicts the larger body of evidence including systematic reviews and should not override the consensus recommendation against its use.
Evidence-Based Alternatives for Cervical Ripening
For Unfavorable Cervix (Bishop Score <5)
Vaginal progesterone (90-mg gel or 200-mg micronized capsules) is recommended for asymptomatic individuals with singleton gestation and transvaginal cervical length ≤20 mm diagnosed before 24 weeks to reduce preterm birth risk. 6
Dinoprostone (prostaglandin E2) gel or insert is indicated for cervical ripening at term, with a single 10 mg vaginal insert releasing approximately 0.3 mg/hour for a maximum of 12 hours. 7, 8
Oral misoprostol 20-25 µg every 2-6 hours results in fewer cesarean sections (RR 0.84) and costs significantly less than dinoprostone, but is absolutely contraindicated in women with prior cesarean delivery due to 13% uterine rupture risk. 7, 9
Mechanical methods (Foley catheter) are preferred in women with cardiovascular disease where prostaglandins are contraindicated. 7
Critical Monitoring Requirements
Continuous fetal heart rate and uterine activity monitoring is mandatory from 30 minutes to 2 hours after prostaglandin administration. 8
Wait at least 30 minutes after removing dinoprostone before starting oxytocin. 7
Allow at least 12 hours after completion of cervical ripening, membrane rupture, and oxytocin use before considering cesarean delivery for "failed induction." 7, 8
Clinical Pitfall to Avoid
Do not recommend evening primrose oil to patients seeking "natural" cervical ripening methods. The evidence demonstrates it is ineffective and potentially harmful, despite its widespread use by some midwives and its availability as an over-the-counter supplement. 4, 1, 2 Instead, counsel patients that evidence-based pharmacologic agents (dinoprostone, misoprostol when appropriate) or mechanical methods are the only proven effective options for cervical ripening.